Regulating system utilizing voltage responsive thyratrons



July 25, 1950 J. M. CAGE 2,516,298

REGULATING SYSTEM UTILIZING VOLTAGE RESPONSIVE THYRATRONS Filed June 20. 1945- @W QMXQU QoX/wx age w %m M Patented July 25, 1950 "UNITED STATES PATENT "OFFICE REGULATING SYSTEM UTILIZING VOLTAGE RESPONSIVE THYRATRONS J ohn M. Cage, Elm Grove, Wis., assignor to Allis- Chalmers Manufacturing Company, Milwaukee, Wis., a corporation of Delaware Application June 20, 1945, Serial'No. 600,509

"of a voltage 'or of another electrical quantity abovea 'nd below a predetermined range of values. The relays may be energized through a pair of *thyr'atrons of which one is responsive to variation of the quantity above a predetermined value andth'e'other 'i'sresponsive to Variation of the quantity 'be'low another predetermined value. Asa 'thy'ratron becomes conductive when the potention of its control grid rises through a value Whioh is close to cathode potential, it is a common expedient to add'to the variable potential impressed on the grid a constant otential of Opposite polarity.

In a "system of the type herein considered it is then advantageous to energize the grids of the pair or thyratrons :rqmapair r voltage dividers, 'each of which provides a variable potential com 'ponent for one of the grids and a, constant po- 'tential component for the other grid. The voltage dividers may include rectifying elements when the voltage impressed thereon is alternating. The cathode filaments of the thyratrons are preferably energized from the circuit to which the voltage dividers are connected to insure that the resume of the thyratrons to the voltage impressed on the voltage dividers will be maintained uniform. The potentials to which the two thyratrons are responsive may be varied simultaneously in opposite senses by a common adjustable edmaeeuon between one or the voltage dividers and the semen grids of the thyratrons. t D

It is generally desirable to delay the response of each thyratron to prevent operation thereof in response to transient voltages accidentally impressed on the voltage dividers. For this purpose each control grid is connected to the associated cathode through a capacitor, but means should be provided to prevent disturbances resulting from charging of the capacitor by the ionic current of the thyratron gri is "carrying eurr'e'nt.

his therefore an ob ect or the present nvention to provide a voltage responsive system including a thyratr'on in which variable and constant 'gjrid boilei'ltial s for the thyia'troll are obtained from the same fs'ource.

Another object of present invention is to provide a voltage responsivesystem including 'a thyratro'ri in when the voltage impressed be d while the thyratron a protective autotransformer l6.

2 tween grid and cathode and the voltage "impressed on the cathode filament are obtained from'the same source.

Another object of the present invention'is to provide a voltage responsive d'e'vice including a 'thyratro'n in which the response of the thyratron to potential variations is delayed toan extent which decreases when the potential variation increases.

Another object of the present invention is to provide a delayed voltage responsive system including a th'yratron in which the thyratron grid ionic current is prevented from disturbing the operation of the time delay means.

Another object of the present invention is to provide a voltage responsive system "in which common means are used for inversely varying the response of a pair of thyratrons todifferent values of voltage.

I Objects and advantages other than those above set forth will be apparent from the following description when read in connection with the accompanying drawing, which diagrammatic'ally illustrates one embodiment of "the present invention applied to the control of a feeder voltage regulator of the tap changing type.

Referring more particularly to the drawing by characters of reference, numeral '6 designates an alternating current generator connected with a distribution'circuit l of 'which the voltage is to be regulated independently of the generator ed with a plurality of taps severally connected with the fixed contacts [2 of a tap changer. The movable contacts H of the tap changer are connectedwith a, regulating winding I5 through Winding 15 may be connected with one or the other fco'ndoctor of circuit 1 through'a selector switch l1 to cause the regulator either to buck or boost the voltage or circuit 1. Winding I5 is inductively related with a winding |'a serially connected with circuit 1 toinduce therein'ia voltage depending on the position of contat'sjll and of switch l1.

Contacts l4 may be actuated by a reversible capacitor motor 2 0 through suitable known means (not shown) for insuring that the movable co tacts always complete any movement thereof initiated by the motor. v 1 M t The operation of regulator Bis controlled by :a voltage'res'p'on'sive system comprising" a pair of current responsive relays 9, 2 for selectively connecting the stator windings of motor 20 with winding II to cause regulator '8 to 'iaiseor lower :;a relatively large delayingcapacitori l'. .itor. 5| may be disconnected from tap 41 by means -.of relay I9, which reconnects capacitor 5| through contact I90 and a'resistor 53 with an 3 the voltage of circuit 1. Relays l9, 2| may be energized "from any suitable source of electric current, and it is generally expedient to supply current to the relays from winding [0 through the secondary winding 22 of a transformer having a primary winding 23 connected across winding l5. The connections of the coil Isa of relay I9 are completed through a current limiting resistor 21 and the plate circuit of a thyratron 28. Coil |9a is shunted by a current smoothin capacitor 29. Coil 21a of relay 2| is likewise connected with winding 22 through a current limiting resistor 3| and the plate circuit of a thyratron 32, and is bridged a current smoothing capacitor 33.

A variable-voltage proportional to the voltage at a predetermined point of circuit 1 is impressed between a pair of conductors 34, 35 from windings I0, 22 through circuit means comprising any suitable known line drop compensator and an adjustable resistor 35. The line drop compensator may comprise, for example, a current transformer 24 energized from circuit 1 and supplying current to an adjustable resistor 25 and anadjustable reactor 26.

. The operation of thyratrons 28, 32 is controlled by means comprising 'apair of voltage dividers connected in parallel across conductors 34, 35. One of the voltage dividers comprises a rectifying device such as a diode 31 having an anode 31a connected with conductor 34' and a cathode 31b connected-with conductor 35-through a resistor 38' and a constant voltage device of any suitable known type such as a battery, a dynamoelectric machine-or, preferably, a dissymetrical glow discharge tube 39. Resistor 38 and tube 39 are bridged by a capacitor 4| for maintaining the potential of cathode 37b at a substantially constant value between successive cycles of the voltage of circuit 1. The other voltage divider comprises a second diode 42 having its cathode 42b connected with conductor 34 and its anode 42a connected with conductor 35 through a second resistor 43 and another constant voltage device such as a second glow discharge tube 44. Resistor 43 and tube 44'are shunted by a capacitor 45 similar to capacitor 4|.

The connections for energizing control grid 280 of 'thyratr0n'28 comprise means for delaying the response of the thyratron to variations in the voltage of circuit 34, 35 includingsuitable impedance means such as a resistor 46 connected between cathode 37b and cathode 44b of tube 44.

An adjustable intermediate point of resistor 46 is connected with grid 280 through a tap 4'1 and through 'a resistor 48,-and is connectedwith conductor,.-35 through a relatively small delaying capacitor; 49-as well as through contact I9d and Capacadjustable tap of a, resistor 52 connected in parallel with tube 44. Contacts-19c, 19d are bridged connect capacitor 59 with resistor 53 through contact 2 I 0. Contacts 2lc, 2|d are bridged by a capacitor 6|. V

The screen grids 28b, 32b of the thyratrons are connected with an adjustable tap of a resistor 62 connected across tube 44. Capacitors 63 to 66 are connected between the grids and the cathodes of the thyratons to prevent undesired operation of the thyratons in response to transient voltages which may accidentally appear in the grid circuits.

To insure uniform response of the system to the voltage of circuit 34, 35 the filaments of the diodes and of the thyratrons are energized from the latter circuit in any suitable known manner. Filaments 28c, 32c may be connected with circuit 34, 35 through a suitable transformer 61. Filaments 31c, 42c may be likewise energized from a filament transformer or may be connected across circuit 34, 35 if they are designed for. the voltage of the circuit. If diodes 31, 42 are disposed in a common envelope they may be provided with a common filament likewise connected between conductors 34 and 35.

It will be apparent that each tapped resistor of the system may comprise an untapped portion connected in series with a tapped portion to improvethe accuracyof the adjustments that may be obtained therewith. One of the conductors of the system, conductor 35 for example, may be grounded to the frame supporting the elements of the system either conductively or through a capacitor 58 for preventing the appearance of disturbing alternating voltage components between the circuits of the system and the frame.

The range of voltage response of the system and the time of response of the thyratrons may be varied in any desired manner by varying the elements of the system. It has been found that the system operated satisfactorily to regulate the voltage of an actual distribution circuit by energizing circuit 34, 35 at 115 volts when the voltage of distribution circuit has the desired value and building the system of elements identified by the following engineering data:

Thyratrons 28, 32 Type 2050 Diodes 31, 42 Type 11726 Glow tubes 39, 44 Type VR /30 Resistor 36 200 ohms Resistors 21, 3| 2,500 ohms Resistor 43 5,000 ohms Resistor 38 7,500 ohms Resistor 53 100,000 ohms Resistor ,52 550,000 ohms Resistors 46, 55 1 megohm Resistor 62 1.5 megohms Resistors 48, 51 2 megohms Capacitors 63, 64, 65, 66 0.002 microfarad Capacitor 68 0.1 microfarad Capacitors 54, 6| 0.25 microfarad Capacitors 49, 58 1 microfarad Capacitors 4|, 45 2 microfarads Capacitors 54, 6| 4 microfarads Capacitors 5|, 59 25 microfarads The operation of the system will first be considered assuming that the voltage at the point of circuit 1 corresponding to the adjustment of the line drop compensator is within the desired range of values for which the system is adjusted. The voltage of winding It) being proportional to the voltage of generator 6 and the voltage of winding 22 being proportional to the regulating voltage supplied to circuit 1 from regulator 8, the voltage impressed on the plate circuits of the thyratrons is proportional to the regulated voltage at the terminals of regulator 8. Under suchconditions the thyratrons are maintained: inoperative by the potentials impressed on the control grids thereof. Current. is, however, supplied to the voltage dividers from windings I 0, 22 through the line drop compensator, resistor 36and circuit 34, 35. As the load-across circuit 34, 35 isconstant, the voltage thereof is also constant and has a predetermined value depending upon. the adjustment of resistor 36.

During thepositivehalf, cycles of the voltage of circuit 1, diode 31 supplies; charging current to capacitor 4| andalso supplies current to resistor 38 andtube 39. During the negative half cycles, the flow of current through. tube 39 is. supplied from capacitor 4| which has a sufficient capacity to maintain the potential of, cathode 311) substantially constant from one cycle to the next. The'potential oix cathode 3112 however. is able to follow the variations of the voltage of circuit 34, 35. in. response to variations in the voltage of circuit I over periods including a relatively large number ofv cycles. Cathode 31b may thus be considered to constitute a source of. variable positive potential for grid 2.80. As the voltage drop in. tube 39 remains substantially constant when the currentthrough. the tube varies within wide limits, anode 3911 may be considered to. constitutea source of constant positive potential for grid 32c.

Likewise anode Mir-constitutes a source of variable, negative,- potential for grid 32c and cathode 44b constitutes a. source of constant negative potential for grid 280.

The potential of tap 41' and of, grid 280 is intermediate the positive and. negative potentials impressed on the. terminals. of. resistor 46 from the voltage dividers, and thepotential of tap, 56 and. of. grid 320 is intermediate thepositive and negative potentials. impressed on, the terminals of resistor 55 from the voltage dividers. The taps of resistors 36, 46, 55. and 62. are so adjusted that when the voltage of circuit I. is within the desired range of values the potentials of grids 26c, 32c are slightly below the critical potentialof the thyratrons so that the thy-ratrons remain nonconductive. This critical potential is negative with. respect to cathode potential in the type of thyratron above identified. Capacitors 54, 6| are charged. under a voltage which is slightly less than the voltage appearing between conductor 35 andthe tap of resistor 52.

As a result of the above described connections, when the voltage of circuit departs from the desired range, the potential of oneof the control gridsis raised and the potential of the other control grid is lowered. When the voltage of circuit 1. rises, the potential of cathode3'lb impressed-on the positive terminalof resistor 46 rises to, a corresponding extent. The negative potential impressed. from cathode 441) onthe negative terminal of resistor 46, however, remains unchanged. The potential of tap 41- and of grid 280 thus rises and will eventually reach the critical potential when the voltage of circuit 1 remains for a sufl'icientlength of time-above a predetermined value, which value is determined by the adjustment. of the taps of resistors 36, 46 and 62. The rise of the potential of grid 28c isdelayed by capacitors 49, 51 which draw chargingcurrentcausing a transient voltage to appear in resistor 46. and temporarily ofifset the. rise in the potential of cathode 31b. The delay in the rise of thepotential of grid 28c to-thecritical valueis relatively large when the increase in the voltage of circuit 1 is relatively small and the delay is relatively small when the increase in the voltage of circuit I is relatively large.

When grid 28c reaches the critical potential, thyratron 28 carries current during every other half cycle of the voltage of circuit I. The thyratron current flows through coil |9a wherein it is rendered suiliciently uniform by the action of capacitor 29 to cause relay I9 to operate and remain in the operated condition as long as the thyratron carries current. Relay I9 closes contact I9b, thereby energizing motor 20, and the motor actuates regulator 8 to the proper position for restoring the voltage of circuit 1 to the desired value.

Relay I9 also disconnects capacitor 5| from tap 4'! and from one of the terminals of capacitor 56 and reconnects capacitor 5| with the other terminal of capacitor t l through contact I90. A transient positive potential component is thereby impressed on tap 41, the initial value of this potential component being the voltage to which capacitor 54 was previously charged from resistor 52. The transient potential component decays as a result of the gradual charge of capacitor 5| from resistor The elements of the system connected with capacitor 5| are so chosen that the transient potential component maintains grid 280 above critical potential during a period of several cycles even if the voltage of circuit 34, 35 decreases to an extent sufiicient to return the grid potential below the critical value. Relay |9 is thus prevented from operating intermittently in response to a rapid succession of intermittent increases of the voltage of circuit '5 above the value for which operation of thyratron 28 is desired.

While thyratron is conducting current the potential. of grid 28c never rises above cathode potential. The grid therefore carries an ionic current which charges capacitors "63 and 49. The capacitance of capacitor 63 however is so small that the charge of the capacitor is completely dissipated through resistors G3 and 46 during the nonconducting half-cycle periods of thyratron 28. Resistor 43 has a resistance of such high value that the charge of capacitor 49 due to the ionic current is likewise negligible and is also dissipated during the nonconducting half-cycle periods of thyratron 28.

During operation of regulator 6, capacitor 5| is connected across a portion of resistor 52 through contacts I90, resistor 53 and conductor 35. The capacitor is then gradually charged at a predetermined portion of the voltage drop in tube 44 whereby the capacitor charge is given a rela tively large negative increment and the capacitor terminal connected with contact I90 is brought to a substantial negative potential. When the voltage of circuit i has been returned to substantially the desired value as a result of the operation of regulator the voltage of circuit 34, 35 is likewise returned to substantially its normal value. The potential of grid 280 i returned below the criticalvalue with a delay determined by the capacitance of capacitor 49, capacitor 5| then having substantially no delaying action as a result of the connection thereof with small capacitor 54. The delay produced by capacitor is small compared to the time required by regulator 8 to move by one step and serves merely to render thy-ratron 2B unresponsive to momentary decreases in thevoltage of circuit "i.

When grid 28c has been returned to a potential iii-16,298

below critical potential, thyratron 28 ceases to carry current, and relay l9 returns to the deenergized position shown. Contact l9?) opens and deenergizes motor 29, which stops and holds regulator 8 in the position reached thereby. Contact, lad recloses to reconnect capacitor with tap 4?. The voltage to which capacitor 5i was ch arged from resistor 52 then depresses the potential of grid 28c below the value corresponding to the actual voltage of circuit 1. lhis depression of the potential of grid 280 is gradually removed while capacitor 5| gradually discharges through resistors 46. Grid 280 thus gradually returns to a potential corresponding to the actual voltage of circuit '3 with a relatively large time delay, whereby regulator 8 is prevented from operating at excessively frequent intervals even if the voltagefoi circuit 1 fluctuates rapidly about the desired value.

When the voltage of circuit 1 decreases below a predetermined value depending on the adjustment of resistors 3t, 55 and 62, the negative potential impressed from anode 42a on one of the terminals of resistor 55 becomes less while the positive potential impressed from anode 39a on the other terminal of resistor 55 remains unchanged. The potential of tap 56 and of grid 32c therefore rises and, if the voltage of circuit 1 remains below the predetermined value for a sufiicient length of time, grid 32c reaches the critical potential of thyratron 32. Current is then supplied to coil Zia through thyratron 32 in the manner above described with respect to coil Ella, and motor is caused to drive regulator B in the proper direction for raising the voltage of circuit 1. The operation of thyratron 32 is then the exact counterpart of the operation of thyratron 28 resulting from a rise in the voltage of circuit 1 and therefore is not described in detail.

The values of the voltage of circuit 1 at which I thyratrons 28 and 32 operate may be adjusted by means of taps ll, 56, which may be used as coarse adjustments of the voltages. A fine adjustment of both voltages in the same sense may be obtained by adjusting the tap of resistor 36. The latter adjustment does not change the value of the voltages of circuit 34, 35 at which the thyratrons operate but varies the ratio between the voltage of circuit 34, 35 and the voltage of circuit 1.

The voltages of circuit l at which thyratrons 23, 32 operate may be varied in opposite senses by adjusting the tap of resistor 62. The latter adjustment varie the potential of screen grids said anode and cathode, a source of variable potential of one polarity, a source of constant potential of the other polarity, said sources having a common terminal connected with said cathode and non-common terminals difiering in potential by the sum of said constant and variable potentials, a resistor connected across said sources of potential, and means comprising a connection between said grid and an adjustable intermediate point of said resistor for rendering said thyratron conductive in response to variation of the said variable potential through a predetermined adjustable value.

2. In a voltage responsive system comprising a source of electric current, the combination of a current responsive device, a thyratron having an anode, a cathode and a control grid, means connecting said device with said source through said anode and cathode, a resistor having a pair of terminals, means connecting said terminals with said source and with said cathode for impressing on one of said terminals a potential of one polarity which varies. with the voltage of said source and for impressing on the other of said terminals a constant potential of the other polarlty from said source, both said polarities being referred to the potential of said cathode to cause said terminals to difi'er in potential by the sum of said constant and variable potentials, and means comprising a connection between said grid and an adjustable intermediate point of said resistor for rendering said thyratron conductive in response to variation of the voltage of said source through a predetermined adjustable value.

3. In a voltage responsive system comprising a source of electric current, the combination of a current responsive device, a thyratron having an anode, a cathode and a control grid, means connecting said device with said source through said anodeand cathode, and means for energizing said control grid comprising a rectifying device, a resistor and a constant voltage device serially connected across said source, a connection between said constant voltage device and said cathode, and means comprising a connection between said grid and the juncture of said recti- 28b, 3217, thereby causing the critical potential of grids 28c, 320 to vary to a corresponding extent. The voltage range within which the voltage of circuit 1 may vary without causing operation of regulator 8 may thus be adjusted while leaving the average value of the voltage unchanged.

Although but one embodiment of the present invention has been illustrated and described, it will be apparent to one skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

1. In a voltage responsive system comprising a source of electric current, the combination of a current responsive device, a thyratron having an anode, a cathode and a control grid, means connecting said device with said source through fying device with said resistor for causing said thyratron to pass abruptly from the non-conductive condition to the conductive condition in response to variation of the voltage of said source through a predetermined adjustable value.

4. In a voltage responsive system comprising a source of electric current, the combination of a current responsivedevice, a thyratron having an anode, a cathode and a control grid, means connecting said device with said source through said anodeand cathode, and means for energizing'said control grid comprising a rectifying device, a resistor and a constant voltage device serially connected across said source, a connection between said constant voltage device and said cathode, a capacitor connected across said resistor and said constant voltage device, and means comprising a connection between said grid and the juncture of said rectifying device with said resistor for causing said thyratron to pass abruptly from the non-conductive condition to the conductive condition in response to variation of the voltage of said source through a predetermined adjustable value.

5. In a voltage responsive system comprising a source of electric current and circuit means for supplying a variable alternating voltage, the combination of acurrent responsive device, a thyratron having an anode, a cathode and a conacrea e ftrol' grid, means connecting said device with said "pacitor connected across saidsecond constant voltage device and said second resistor, connect-ions between said constant voltage devices and the cathode of said thyratron, connections from said rectifying devicesand thecathode of said thyratron to saidcircuit :means, a connection between the point of juncture of one of said resistors with the associated said rectifying device and the point of juncture of the other of said resistor with the associated said constant voltage device including a third resistor, and means comprising a connection between saidcontrol grid and an adjustable point of said third resistor for rendering, said thyratron conductive in response to variation of the voltage of said circuit means through a predetermined adjustable value.

6. In a voltage responsive system comprising a source of electric current and circuit means for supplying a variable alternating voltage, the combination of a current responsive device, a thyratron having an anode, a cathode, a control grid and-a screen grid, means connecting said device with said source through said anode; and

cathode, and meansfor energizing said control grid comprising a first rectifying device having.

an anode and a cathode, a first constant voltage device, and a first resistor connecting said first constant voltage device with the cathode of said first rectifyingdevice, a first capacitor connected across saidfirst constant voltage device and said first resistor, a second rectifying device having an anode and 'a cathode, a secondconstant voltage device and a second resistor connecting said second constant. voltage device with the anode of said second rectifying device, a second capacitor connected across said second constant voltage device and said second resistor, connections between said constant voltage devices and the cathode of said thyratron, connections from said rectifying devices and the cathode of said thyratron to said circuit means, a connection between the point of juncture of one of said resistors with the associated said rectifying device and the point of juncture of the other of said resistors with the associated said constant voltage device including a third resistor,-a connection between said control grid and an adjustable point of said third resistor for rendering said thyratron conductive in response to variation of the voltage of said circuit means through a predetermined adjustable value, and means for varying said predeter-mined value comprising a fourth resistor connected across the second said constant voltage 'device and a connection between said screen grid and an adjustable intermediate point of said fourth resistor.

IQIna voltage responsive system comprising a source of electric current, circuit means forsupplying a variable alternating voltage, and a translating-device, the combination of a' pair of current responsive devices for selectively controlling said translating device, a pair of thyratrons, each said thyratron comprising an anode, a cathode and a control grid, means connecting one of said current responsive devices with said source through one of said thyratrons, means connecting the other of said current responsive devices with said source through the other of said thyratrons, and means for energizing the control grids of said thyratrons comprising a first rectifying device having an anode and a cathode, a first constant voltage device, and a first resistor connecting said first constant voltage device with the cathode of said first rectifying device, a first capacitor connected across said first constant voltage device and said first resistor, a second rectifying device having an anode and a cathode, a. second constant voltage device-and a second resistor connecting said second constant voltage device with the anode'o'f said second rectifying device, a second capacitor connected across said second constant voltage device and'said second resistor, connections between said constant voltage devices and the cathodes of said thyratrons, connections from said rectifying devices and the cathodes of said thyratrons to said circuit means, a connection between the point of juncture of said first resistor with said first rectifying device and the point of juncture of said second resistor with said second constant voltage device comprising a third resistor, a connection between the point of juncture of said second resistor with said second rectifying device and the point of juncture of said first resistor with said first constant voltage device comprising a fourth resistor, and means comprising connections between the control grids of said thyratrons and adjustable points of said third and fourth resistors for selectively rendering said thyratrons conductive in response to variation of said alternating voltage above and below a predetermined adjustable range of values.

'8. In a voltage responsive system comprising a source of electric current, circuit means for supplying a variable alternating voltage, and a translating device, the combination of a pair of current responsive devices for selectively controlling said translating device, a pair of thyratrons, each-said thyratron comprising an anode, a cathode, a control grid and a screen grid, means connecting one of said current responsive devices with said source through one of said thyratrons, means connecting the other of said current responsive devices with said source through the other ofssaid thyratrons, and means for energizing the control grids of said thyratrons comprising a first rectifying device having an anode and a cathode, a first constant voltage device, and a first resistor connecting said first constant voltage device withthe cathode of said first rectifying device, a first capacitor connected across said first constant voltage device and said first resistor, a secondrectifying device having an anode and a cathode, a second constant voltage 'device and a second resistor connecting said second constant Voltage device with the anode of said second rectifying device, a second capacitor connected across said second constant voltage device and said second resistor, connections between said constant voltage devices and the cathodes of said thyratrons,connections from said rectifying devices and the cathodes of said thyratrons to said circuit meansga connectionbetween the point of juncture ofsaid first resistor with saidlfirst rectifyingdevice and the point of juncture of said second resistor with said second constant voltage device comprising a third resistor, a connection between the point of juncture of said second re- ;sistor with said second rectifying device and the point of juncture of said first resistor with said firstconstant voltage device comprising a fourth resistor, means comprising connections between the control grids of saidthyratrons and adjustable points of said third and fourth resistors for selectively rendering said thyratrons conductive in response to variation of said alternating voltage above and below a predetermined adjustable range of values, and means for adjusting the magnitude of said range of values comprising a fifth resistor connected across the second said constant voltage device and a common connection between the screen grids of said thyratrons and anadjustable intermediate point of said fifth -resistor..

tial, a connection between said grid and an adjustable intermediate point of said resistor for rendering said thyratron conductive in response to variation of the said variable potential through a predetermined adjustable value, and means for delaying the response of said thyratron comprising a capacitor connected between said intermediate point of said resistor and said cathode.

10. In a voltage responsive systemcomprising a source of electric current, the combination of a current responsive device, a thyratron having an anode, a cathode and a control grid, means connecting said device with said source through said anode and cathode, a source of variable potential,

of one polarity, a, source ofconstant potential of the other polarity, said sources having a common terminal connected with said cathode and noncommon terminals diifering in potential by the sum of said constant and variable potentials, a-

resistor connected across said sources of potential, and means including a connection'between said grid and an intermediate point of said resistor for causing said thyratron to become conductive in response to variations in said variable potential after a time period which decreases when said potential departs from a predetermined adjustable value by an increasingamount.

11. In a voltage responsive system comprising a source of electric current and circuit means for supplying a variable voltage, the combination of a first current responsive device, a first thyratron having a control grid, means connecting said first current responsive device with said source through said first thyratron, an adjustable connection between the control grid of said first thyratron and said circuit means for rendering said first thyratron conductive in response to variation of said voltage above a first predetermined adjustable value, a second current responsive device, a second thyratronhaving a control grid, means connecting said second current responsive device with said source through said second thyratron, an adjustable connection between the control grid of said second thyratron and said circuit means for rendering saidsecond thyratron conductive in response to variationof said voltage below ,a second predetermined adjustable value, and an adj ustable common connection between said first and secondthyratrons and said circuit meansior simultaneouslyIadjusting said first andsecond voltage values. I

-.,l 2. In a voltage responsive system comprising a source of electric current and circuit means for supplying a variable voltage, the combination of a first current responsive device, a first thyratron having a control grid, means connecting said first currentresponsive device with said source through said first thyratron, an adjustable connection between the control grid of said-first thyratron and said circuit means for rendering said first thyratron conductive in response to variation of said voltage above a first predetermined adjustable value, a second current responsive device, a second. thyratron having ,a control grid, means connecting said second. current responsive device with said source through said second thyratron, an adjustable connection between the control grid of said second thyratron and said circuit means forv rendering said second thyratron conductive in response to variationof said voltage below a second predetermined adjustable value, and an-adjustablecornmon connectionbetween said first and second thyratrons and said circuit means for simultaneously adjusting said first and second voltage values by raising one of said valu s and lowering the other of said values. g

13. In a voltage responsive system comprising a source of electric current and circuit means for supplying a variable voltage, the combination of a first current responsive device, a first thyratron having a control grid and a screen grid, means connecting said first-current responsive device with said source through said first thyratron, an adjustable connection between the control grid of said first thyratron'and said circuit means for rendering said'first thyratron conductive in response to variation of said voltage above a first predetermined adjustable value, a second current responsive device, a' second thyratron having, a control grid and a screen grid, means connecting said second current responsive device with said source through said second thyratron, an adjustable connection between the control grid of saidsecond thyratron and said circuit means for rendering said second thyratron conductive 'in response to variation of said voltage below a, second predetermined adjustable value, and an adjustable common connection between said screen grids of said thyratrons and said circuit means for simultaneously adjusting said first'and second values.

JOHN'M. CAGE.

' REFERENCES CITED The followingreferences are .of record in the file of this patent:' I 

